1. Field of the invention
The present invention generally relates to an improvement in the production of 2-keto-L-gulonic acid. More particularly, it concerns a method of preparation of said acid from 2,5-diketo-D-gluconic acid through microbial conversion.
2. Description of the Prior Art
The 2-keto-L-gulonic acid which is useful as an intermediate for synthesizing L-ascorbic acid has hithertofore been commercially produced by the so-called "Reichstein's method", which is known as a technically established process.
This method, however, comprises a number of complex steps and therefore any improvement in the overall yeild is very difficult if not completely impossible. There has hitherto been a number of proposals which contemplate a reduction in the number of steps and/or an improvement in the overall yeild.
For instance, a biochemical method wherein the 5-keto-D-gluconic acid is reduced to obtain selectively L-idonic acid which is subsequently oxidized to 2-keto-L-gulonic acid, a method of direct microbial conversion of L-sorbose into 2-keto-L-gulonic acid and the like are already known in the art.
These proposed methods have succeeded in the reduction in the number of the steps required for the production of 2-keto-L-gulonic acid at least theoretically but unexceptionally failed in the actual improvement in the overall yield and in the feasibility or the steady operation of the total system.
Moreover, the attendant disadvantageous abundance of the resultant by-product both in terms of the kind and the quantity thereof and difficulty in the separation of the intended product from the mixture which contains the by-products, and complexity in the operation hinder the commercialization of these processes.